Steel Bar Grating Sizes - Load Tables, Weight & Selection Guide

Steel bar grating is a structural flooring product consisting of parallel bearing bars joined by cross bars at regular intervals. It is used extensively for industrial platforms, walkways, stair treads, trench covers, mezzanine decks, and catwalks where an open flooring surface is required for drainage, ventilation, or light passage. Unlike solid plate flooring, bar grating reduces dead load on the supporting structure while providing slip resistance and allowing debris and liquids to pass through.

Grating selection depends on three variables: bearing bar size and spacing (which determine load capacity), cross bar spacing (which affects lateral stability and local point-load distribution), and material and finish (which govern corrosion resistance). This guide covers standard NAAMM designations, load tables for common grating types, weight data, and practical selection criteria.

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Standard grating designations (NAAMM system)

The National Association of Architectural Metal Manufacturers (NAAMM) MBG-531 standard defines the designation system for metal bar grating. A typical designation such as 19-W4 encodes three pieces of information:

• 19 = bearing bar spacing in sixteenths of an inch. 19 means 19/16 inch (1-3/16 inch) center-to-center spacing between bearing bars.
• W = construction type: W for welded, S for swage-locked, P for press-locked, R for riveted.
• 4 = bearing bar depth in increments of 1/4 inch. 4 means a 1-inch deep bearing bar (4 x 1/4 = 1 inch).

The bearing bar thickness is not encoded in the designation and must be specified separately. Standard thicknesses are 1/8 inch (light duty), 3/16 inch (medium duty), and 1/4 inch (heavy duty). For most industrial applications, 3/16 inch thickness is standard.

Reading a designation: 38-W4 = 3-3/16 inch bar spacing, welded construction, 1 inch deep bearing bars. The wider spacing makes this a lighter panel suitable for pedestrian traffic where point loads are limited.

Common grating designations - size, spacing, and weight

The table below lists the most common carbon steel grating designations with their key dimensions and approximate weight per square foot. All weights assume 3/16 inch thick bearing bars unless otherwise noted.

Notes on the table:

• Closer bar spacing (lower first number) increases weight and load capacity. 11-series grating has roughly 70% more bearing bars per foot than 19-series.
• Deeper bearing bars (second number indicates depth in quarter-inches) increase bending capacity without changing the spacing. Moving from W4 (1 inch depth) to W2 (1-1/2 inch depth) roughly doubles the load capacity.
• Heavy-duty (HD) designations use 1/4 inch bar thickness for forklift and vehicular traffic applications.

Load tables by span

Load capacity of bar grating is governed by the bending strength of the bearing bars across the clear span between supports. The tables below show allowable uniform load (psf) and maximum concentrated load (lbs per foot of width) for 19-W4 grating (1 inch deep, 3/16 inch thick, 1-3/16 inch spacing) at various clear spans. Values are based on A36 steel with Fy = 36 ksi and a deflection limit of L/240.

19-W4 - Allowable uniform load (psf)

19-W4 - Maximum concentrated load (lbs per foot of width)

15-W4 - Allowable uniform load (psf)

For spans beyond 6 feet, most grating types require intermediate support or heavy-duty designations with deeper bearing bars. Consult the manufacturer load tables for specific project conditions.

Weight per square foot

Grating weight directly affects the dead load on supporting beams and the total cost of the flooring system. The following table provides weight per square foot for common designations in carbon steel.

Weight estimation formula: Weight (psf) = (bar depth x bar thickness x bars per foot) x 3.4 (steel density factor) + cross bar contribution. For approximate estimating, cross bars add roughly 0.5 to 1.0 psf depending on spacing.

When calculating total dead load for grating-supported platforms, add 1-2 psf for clip attachments and fasteners. If the grating is galvanized, add approximately 3-5% to the mill finish weight to account for the zinc coating.

Grating types comparison

Four primary construction methods are used for steel bar grating, each with distinct advantages. The choice depends on load requirements, aesthetic preferences, fabrication capabilities, and budget.

Welded grating is the most common type, accounting for roughly 75% of all grating installed in North America. The electro-forged weld at each cross bar intersection provides high structural rigidity. It is available in the widest range of sizes and is the most economical choice for standard industrial flooring.

Swage-locked grating uses cross bars that are mechanically pressed into pre-notched bearing bars, creating a tight mechanical joint without welding. This method allows the use of rectangular or I-shaped cross bars that provide a more refined appearance. It is common in architectural applications and where a clean, uniform top surface is desired.

Press-locked grating is similar to swage-locked but both the bearing bars and cross bars are notched before assembly. This produces a very flat, uniform surface suitable for architectural panel applications. It is available in both steel and aluminum.

Riveted grating uses rivets at each intersection for maximum impact resistance and fatigue life. It is the preferred choice for bridge decks, highway applications, and locations subject to heavy wheeled traffic. The riveted construction distributes loads across more bars than welded construction.

Common applications

For stair treads, most specifications require a closed checker plate nosing along the leading edge and a minimum 1-1/2 inch deep bearing bar. Tread width is typically 10-12 inches. The nosing improves traction and visually defines the step edge.

Trench covers subject to vehicular traffic require heavy-duty designations and must be checked against AASHTO H-20 or HS-20 wheel loads. For pedestrian-only trench covers, 19-W4 at 2-3 foot spans is typically sufficient.

Materials

Carbon steel (ASTM A36 / A1011)

Carbon steel is the default material for industrial grating. ASTM A36 (Fy = 36 ksi) is used for hot-rolled bars, and ASTM A1011 SS Grade 36 is used for cold-formed bars. Carbon steel grating must be protected from corrosion by galvanizing or painting for most service environments. It is the most economical option, with material costs roughly 40-60% lower than stainless steel equivalents.

Stainless steel (304 / 316)

Stainless steel grating is specified for corrosive environments: chemical plants, food processing, marine applications, and wastewater treatment. Type 304 (18% Cr, 8% Ni) provides general corrosion resistance. Type 316 (16% Cr, 10% Ni, 2% Mo) adds molybdenum for superior resistance to pitting corrosion in chloride environments. Stainless grating weighs approximately the same as carbon steel (density difference is negligible at 0.29 lb/in3 vs 0.283 lb/in3), but costs 3-5 times more.

Aluminum (6061-T6 / 6063-T6)

Aluminum grating is used where weight savings are critical: rooftop platforms, marine applications, and areas where corrosion resistance is needed without the cost of stainless steel. 6061-T6 is the standard structural alloy (Fy = 35 ksi). 6063-T6 is used for architectural applications where appearance matters. Aluminum grating weighs roughly one-third of carbon steel grating in the same designation, but load capacity is also reduced due to the lower modulus of elasticity (E = 10,100 ksi vs 29,000 ksi for steel).

Surface treatments

Hot-dip galvanizing per ASTM A123 is the most common corrosion protection for carbon steel grating. The zinc coating thickness is typically 2.0-3.5 mils depending on material thickness. Galvanizing adds approximately 3-5% to the grating weight and slightly increases the bearing bar dimensions, which may affect fit in tight openings.

Serrated surface treatment cuts diagonal notches into the top of each bearing bar to improve slip resistance. It is required for oily or wet environments and is available on all grating types. Serrated grating is specified in oil refineries, chemical plants, and outdoor platforms subject to ice accumulation.

Frequently Asked Questions

What is the most common steel grating size? 19-W4 (1-3/16 inch bar spacing, welded, 1 inch deep bearing bars) is the most widely used grating designation in North America. It balances load capacity, weight, and cost for typical industrial and commercial applications. For pedestrian walkways and light platforms, 19-W4 at 3-4 foot spans is standard.

How do I select grating for forklift traffic? Forklift traffic requires heavy-duty grating with minimum 1-1/2 inch deep bearing bars at 1/4 inch thickness. Designations such as 11-W2 (HD) or custom configurations with 2 inch deep bars are common. The grating must be checked for concentrated wheel loads per AASHTO criteria, and spans are typically limited to 2-3 feet. Serrated surface treatment is recommended for traction.

What span is safe for walkway grating? For standard 19-W4 grating supporting pedestrian loads (100 psf live load), the recommended maximum span is 4 feet. This keeps deflection within L/240, which is the standard comfort criterion for pedestrian walkways. For ADA-compliant walkways where vibration sensitivity is a concern, reducing spans to 3 feet provides a stiffer platform.

Does galvanizing affect grating load capacity? No. The hot-dip galvanizing process per ASTM A123 does not reduce the structural capacity of the bearing bars. The zinc coating is thin (2-3.5 mils) and does not contribute to, nor detract from, the bending strength of the steel bars. However, galvanizing does slightly increase overall dimensions, which may affect fit in close-tolerance applications.

How does aluminum grating compare to steel for the same load? Aluminum grating in the same nominal designation (for example, 19-W4) has roughly one-third the weight of carbon steel but also lower load capacity because aluminum modulus of elasticity (10,100 ksi) is about one-third of steel (29,000 ksi). To match the deflection performance of steel grating, aluminum typically requires a deeper bearing bar. For equal stiffness, an aluminum bar must be approximately 1.4 times deeper than a steel bar.

What is the difference between close mesh and standard grating? Close mesh grating (11-series or closer) has bearing bar spacing of 11/16 inch or less. The tighter spacing reduces the open area and increases the number of bearing bars per foot, providing higher load capacity and smaller openings. Close mesh is required for applications where small objects must not fall through the grating, such as mezzanine floors above occupied spaces, or where heel-proof surfaces are needed for pedestrian traffic.

Run This Calculation

Steel Weight Calculator -- calculate the total weight of grating panels for your project based on designation, dimensions, and quantity.

Beam Capacity Calculator -- check the supporting beams under grating dead load plus the specified live load.

Related pages

• Steel weight calculator
• Beam capacity calculator
• Steel density table
• Steel grades
• Beam sizes
• Plate weight
• Floor systems
• Tools directory
• Reference tables directory
• Disclaimer (educational use only)

Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice, a design service, or a substitute for an independent review by a qualified structural engineer. All load tables, weights, and values shown are approximate and based on NAAMM MBG-531 general data with standard assumptions. Actual capacity varies by manufacturer, material certification, and installation conditions.

All real-world structural design depends on project-specific factors (loads, combinations, stability, detailing, fabrication, erection, tolerances, site conditions, and the governing standard and project specification). You are responsible for verifying inputs, validating results with an independent method, checking constructability and code compliance, and obtaining professional sign-off where required.

The site operator provides the content as is and as available without warranties of any kind. To the maximum extent permitted by law, the operator disclaims liability for any loss or damage arising from the use of, or reliance on, this page or any linked tools.